This invention relates in general to illuminated display units and in particular to a new and useful display unit to be used as a house number, traffic sign, advertisement carrier or the like, having a fluorescing photoconductive plate, into which is fitted at least one light-emitting diode at at least one lateral limiting edge.
Such a display unit is known from German OS 33 22 393. In the light fixture described therein, light-emitting diodes are inserted into a diffusing lens from the narrow edges so as to admit the light into the lens as fully as possible. It can be inferred from FIG. 1 that thereby a symbol is illuminated from behind, so that a contrast results. In such a case however, the light yield is very small, so that this arrangement is not suitable for example for relatively large display areas.
Also from U.S. Pat. No. 4,373,284 or U.S. Pat. No. 4,484,104 it is known, for example, how to illuminate the plate carrying the respective symbols from behind, so that the information stands out through different coloration or different light transmission. Further it is known practice to form the symbols themselves, for example a legend, by an appropriately formed light-emitting tube according to Swiss Patent 168,894, or according to German patent 30 49 064 light-emitting elements are strung together according to the shape of the symbols.
All of the known display units have the disadvantage of relatively high current consumption, so that when operating with solar cells, a large number of solar cells and a large storage capacity are required.
Further, from German OS 36 02 819 a display unit is known where the light-emitting elements are incorporated in a fluorescing photoconductive plate so as to illuminate display symbols from behind. This known solution does indeed represent an improvement over the previous solutions with respect to energy requirement but it is still not low enough. Another disadvantage is that the photoconductive plate must have a curved reflection surface, so that commercially available plates cannot be used and manufacture becomes complex and expensive. Without this curved reflection surface a fairly uniform illumination of large display areas would not be ensured.
It is indeed known from German OS 23 56 947 to apply symbols on the back of a transparent plate, but also with this known arrangement the light yield is very low, as the light must enter from the side through an outside edge of the plate with losses by reflection, and no contrast area is provided. Moreover, in ordinary transparent plates no special emergence of light at contact points is observable.